Technical Abstract:
The necrogenic enterobacterium, Erwinia amylovora (Ea) is the causal agent of the fire blight (FB) disease of many Rosaceae species, including apple and pear. During the infection process, the bacteria induce an oxidative stress response with kinetics similar to those induced in an incompatible bacteria-plant interaction. In order to understand the mechanisms that distinguish resistant and susceptible responses in FB resistant and susceptible apple genotypes after inoculation with Ea, differentially expressed genes were identified by cDNA-AFLP analysis. cDNA was isolated from M.26 (susceptible) and Geneva 41 (G.41, resistant) apple tissues collected 2 and 48h after challenge with a virulent Ea strain or mock (buffer) inoculated. In the AFLP experiments, M.26 and G.41 showed different patterns of expression, including genes specifically induced, not induced, or repressed by Ea. In total, 198 EST's differentially expressed between M.26 and G.41 were identified using 42 pairs of AFLP primers. cDNA-AFLP analysis of global EST expression in a resistant and a susceptible apple genotype identified several major classes of genes. Sequencing data for the ESTs showed that host genes linked to resistance, including proteins involved in perception, signaling, defense and apoptosis, were modulated by Ea. Thirty genes were identified by a bioinformatics study to be specifically involved in the interaction Malus / E. amylovora and not in any other reported biotic or abiotic reaction. Mapping of these ESTs is in progress. This project is supported by a National Research Initiative Competitive Grant 2005-35300-15462 from the USDA Cooperative State Research, Education, and Extension Service.